1. Field of the Invention
The invention relates to a method and a device for regulating process gases for heat treatments of metal materials/workpieces in industrial furnaces, which have at least one treatment chamber, at least one burnoff point having gastight closable valve, and a pressure regulator, at least one component of the respective process gas being prepared in at least one process-relevant range of dimensions.
2. Description of the Related Art
In general, it is known in industrial furnaces that, for example, in the case of typical carburization gassing, the flushing method is applied. I.e., an established quantity of protective gas is permanently supplied to the furnace continuously and is exhausted from the furnace while being burned off (flared off) at a burnoff point. This flushing is necessary in order to achieve a quasi-stationary equilibrium state in the atmosphere through mixing of continuously newly supplied protective gas and/or natural gas-air mixtures and thus be able to regulate the carbon (C) potential.
On the one hand, the thermal loss during flare off of the protective gas at the burnoff and, on the other hand, the actual gas loss, which must be compensated for by new components of the process gas, are disadvantageous in this continuous furnace flushing technique. In addition, the burnoff gas has a C potential previously defined by the regulator, which is also no longer usable and is simply burned off.
According to DE 10 2008 029 001.7 B1, the processing effect of the gas control in industrial furnaces was improved in that, to save protective gas and reduce heating energy losses, a hydrocarbon was supplied on demand for the carburization and the C potential in the protective gas was regulated and reactions which cannot be regulated and/or are undesired were prevented. A novel protective gas recirculation system was thus provided for gas carburization. The components carbon dioxide, oxygen, and water vapor react therein in a preparation chamber of an industrial furnace with a supplied hydrocarbon to in turn form carbon monoxide and hydrogen, in a catalytically supported manner. The regeneration of already “consumed” protective gas, i.e., a protective gas having a low C potential, is advantageously thus achieved. The C potential regulation occurs in the preparation chamber of the treatment chamber. The “prepared” protective gas can then be fed back into the treatment chamber at one or more points, so that a real cycle results for the gas carburization.
The protective gas is regularly no longer burned off, but rather supplied by recirculation back to the heating chamber, after it has passed through an intermediate step, the preparation, in an internal or external preparation chamber. It is thus no longer flushed as previously, but rather reused.
Through the carburization inside the heating chamber, the concentrations of CO2, H2O, and O2 rise and the C level drops. This depleted gas is not combusted, but rather conducted using a circulator into the mentioned preparation chamber, which is locally separated from the heating chamber. A C level enrichment occurs here through the finely-dosed addition of natural gas, the following reactions occurring and the concentrations dropping again.
The gasification method cited according to DE 10 2008 029 001.7 B1 was refined according to DE 10 2009 038 598.3 in that the generation and enrichment of the protective gas can be performed in this case as a separate preparation and separated from the batch. The batch can thus always have a homogeneous gas atmosphere applied thereto.
However, for process-related and also safety-technical reasons, industrial furnaces still require a burnoff point having gastight closable valve and a pressure regulator, which is not predominantly used for permanent flare-off, but must also include the function of explosion safety, during the performance of heat treatments using the process gases described, for example. Known burnoff points in this context are functionally characterized by a permanent gas flow and thus by disadvantageously high gas losses according to internally known prior art. This is mechanically solely solved in that an overpressure flap, which is not terminated completely gastight, is provided for dissipating overpressure occurring in the furnace chamber, this flap not being regulated in the normal case, but rather at best being opened according to rigidly set experiential values.